BALTIMORE — NASA will be sending aircraft over the Baltimore-Washington region starting next week to help improve how satellites track air pollution.

Satellites already monitor many components of air pollution, but researchers said Thursday that it is difficult to use measurements from space to detect pollution near the ground. The multi-year study is designed to help improve the ability of satellites to measure conditions near the surface.

The flights will use two aircraft, one flying at higher altitude to take readings similar to those gathered by satellites, which pass over once a day, and the other at lower altitudes. The flights will be coordinated with six ground observation sites from the D.C. Beltway to northeast of Baltimore. A four-engine turboprop P-3B that recently returned from Antarctica will fly low over the state, flying a corkscrew pattern over the ground stations at altitudes between 1,000 and 15,500 feet. The second aircraft, a UC-12, will cruise at about 26,000 feet.

Both will measure ozone, soot and other particulate matter. The P-3B will also track pollutants that lead to the formation of ozone such as nitrogen dioxide and formaldehyde. In addition to the ground stations, the P-3B's flight path will also take it over Interstate 95 and the Baltimore-Washington Parkway.

Researchers hope the results will improve forecasting, tracking of pollution sources and changes in emissions over time, said Jim Szykman, a research engineer at the U.S. Environmental Protection Agency Office of Research and Development.

Maryland, for example, experiences about 35 days a year where air quality exceeds health standards, with much of the pollution coming from outside the state, said Dave Krask, an atmospheric chemist with the Maryland Department of the Environment.

"On some of Maryland's worst air quality days, the air high above the ground, floating into the state is already at levels approaching the health standards, so it doesn't take much in terms of local emissions to push us over the limit," Krask said.

The Baltimore-Washington region is the first of four where aircraft will be used to help improve satellite measurements.

Flyovers are planned in 2013 over Houston, and winter flyovers are also planned over parts of California. Results of the first three flyovers will be used to help choose the fourth location, although Los Angeles, Birmingham, Ala. and Atlanta are being considered, said Jim Crawford, the project's principal investigator and a researcher at NASA's Langley Research Center in Hampton, Va.

The Baltimore-Washington area flyovers are expected to provide results applicable to other northeastern metropolitan areas such as Philadelphia, New York and Boston.

The other areas differ in industry and geography. Houston, for example, has a large petrochemical industry while in California agricultural practices and wood-burning also influence air quality, Crawford said.